Practical and safe fluorination of white phosphorus (P4)

The hexafluorophosphate anion is a key component in the most commonly used electrolyte in lithium-ion batteries, which is lithium hexafluorophosphate (LiPF6). Typically, LiPF6 is produced through a sequence of multi-step reactions involving white phosphorus, chlorine gas, and hydrogen fluoride. These processes require costly safety measures when carried out on an industrial scale, making them a significant factor in the overall production costs of batteries.

The oxidative fluorination of phosphorus tetramer (P4) and its red allotrope is carried out using a common and easy-to-handle oxidant, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The reaction can proceed through either a phosphorus(III) or phosphorus(V) intermediate. Additionally, the phosphorus(III) intermediate can be functionalized by selected nucleophiles, such as alcohols or amines, resulting in the formation of phosphites or aminophosphines, respectively. The semi-hydroquinone radical anion form of DDQ (DDQ•–) can be isolated and re-oxidized back to DDQ using inexpensive oxidants such as oxygen or nitric acid, or through electrochemical means.